Sandvik 8R40

Disclaimer: Recommendations are for guidance only, and the suitability of a material for a specific application can be confirmed only when we know the actual service conditions. Continuous development may necessitate changes in technical data without notice. This datasheet is only valid for Sandvik materials.

Sandvik 8R40 is an austenitic, niobium-stabilized stainless chromium-nickel steel for use at temperatures up to 850°C (1560°F).

Standards

ASTM: TP347, TP347H

UNS: S34700, S34709

EN Number: 1.4550, 1.4912

EN Name: X6CrNiNb18-10, X7CrNiNb18-10

W.Nr.: 1.4550

DIN: X 6 CrNiNb 18 10

SS: 2338

AFNOR: (Z6CNNb 18.10)

BS: 347S31, 347S51

Product standards

Seamless tube and pipe:

ASTM A213, A269, A312, A376

EN 10216-5

BS 3059 Part 2, BS 3605 Part 1, BS 3606

DIN 17456,17458

SS 14 23 38

Chemical composition (nominal) %

Chemical composition (nominal) %

C

Si

Mn

P

S

Cr

Ni

0.06

0.4

1.8

≤0.040

≤0.015

17.5

11

Nb=≥10xC

Forms of supply

Seamless tube and pipe - Finishes and dimensions

Seamless tube and pipe in 8R40 is supplied in dimensions up to 260 mm outside diameter in the solution-annealed and white-pickled condition or in the bright-annealed condition.

Mechanical properties

For tube and pipe with wall thicknesses greater than 10 mm (0.4 in.) the proof strength may fall short of the stated values by about 10 MPa (1.4 ksi).

At 20°C (68°F)

Proof strength

Tensile strength

Elong.

Hardness Vickers

Rp0.21)

Rp1.01)

Rm

A2)

approx.

MPa

ksi

MPa

ksi

MPa

ksi

%

≥220

≥32

≥250

≥36

515-690

75-100

≥40

155

1 MPa = N/mm2 1) Rp0.2 and Rp1.0 correspond to 0.2% offset and 1.0% offset yield strength, respectively. 2) Based on L0 = 5.65 √S0 where L0 is the original gauge length and S0 the original cross-section area.

Impact strength

Due to its austenitic microstructure, Sandvik 8R40 has very good impact strength both at room temperature and at cryogenic temperatures.

Tests have demonstrated that the steel fulfils the requirements (60 J (44 ft-lb) at -196 oC (-320 oF)) according to the European standards EN 13445-2 (UFPV-2) and EN 10216-5.

At high temperatures

Metric units

Temperature

Proof strength

Rp0.2

Rp1.0

°C

MPa

MPa

min.

min.

50

195

232

100

175

210

150

165

195

200

155

185

250

147

175

300

139

167

350

133

162

400

129

159

450

126

156

500

124

155

550

118

152

600

-

-

Imperial units

Temperature

Proof strength

Rp0.2

Rp1.0

°F

ksi

ksi

min.

min.

100

29.2

36.0

200

25.7

30.7

300

24.1

29.7

400

22.3

28.1

500

21.2

25.2

600

19.9

24.1

700

19.0

23.4

800

18.3

22.8

900

18.0

22.2

1000

17.3

22.0

1100

16.8

21.8

Creep rupture strength

Temperature

10 000 h

100 000 h

°C

°F

MPa

ksi

MPa

ksi

approx.

approx.

approx.

approx.

540

1005

253

36.7

186

27.0

550

1020

237

34.4

172

24.9

580

1075

192

27.8

135

19.6

600

1110

166

24.1

115

16.7

620

1150

142

20.6

97

14.1

650

1200

112

16.2

74

10.7

670

1240

96

13.9

61

8.8

700

1290

74

10.7

48

7.0

800

1470

28

4.1

16

2.3

Physical properties

Density: 7.9 g/cm3, 0.29 lb/in3

Thermal conductivity

Temperature, °C

W/m °C

Temperature, °F

Btu/ft h °F

23

14

73

8

100

15

200

8.5

200

17

400

10

300

18

600

10.5

400

20

800

11.5

500

21

1000

12.5

600

23

1100

13

Specific heat capacity

Temperature, °C

J/kg °C

Temperature, °F

Btu/lb °F

23

485

73

0.11

100

500

200

0.12

200

515

400

0.12

300

525

600

0.13

400

540

800

0.13

500

555

1000

0.13

600

575

1100

0.14

Thermal expansion 1)

Temperature, °C

Per °C

Temperature, °F

Per °F

30-100

17

86-200

9.5

30-200

17.5

86-400

9.5

30-300

17.5

86-600

10

30-400

18

86-800

10

30-500

18.5

86-1000

10.5

30-600

18.5

86-1200

10.5

30-700

19

86-1400

10.5

30-800

19.5

86-1600

11

30-900

19.5

86-1800

11

30-1000

20

1) Mean values in temperature ranges (x10-6)

Modulus of elasticity 1)

Temperature, °C

MPa

Temperature, °F

ksi

20

200

68

29.0

100

194

200

28.2

200

186

400

26.9

300

179

600

25.8

400

172

800

24.7

500

165

1000

23.5

1) (x103)

Corrosion resistance

Sandvik 8R40 has with some limitations (nitric acid) the same resistance as the unstabilized steel ASTM 304, i.e. the material has good resistance in:

Organic acids at moderate temperatures

Salt solutions, e.g. sulphates, sulphides and sulphites

Caustic environments at moderate temperatures

Sandvik 8R40 is generally used at temperatures above 500 °C (930 °F), however, where wet corrosion is not relevant.

Intergranular corrosion

The stabilization with niobium gives Sandvik 8R40 good resistance to intergranular corrosion.

Pitting and crevice corrosion

The steel may be sensitive to pitting and crevice corrosion even in solutions of relatively low chloride content.

Stress corrosion cracking

Austenitic steels are susceptible to stress corrosion cracking. This may occur at temperatures above about 60°C (140°F), if the steel is subject to tensile stresses and at the same time comes into contact with certain solutions, particularly those containing chlorides. Such service conditions should therefore be avoided. Conditions when plants are shut down must also be considered as the condensates which are then formed can develop a chloride content that leads to both stress corrosion cracking and pitting.

Gas corrosion

Sandvik 8R40 can be used in

Air up to 850°C (1560°F)

Steam up to 750°C (1380°F)

Synthesis gas (ammonia synthesis) up to about 550°C (1020°F)

Creep behavior should also be taken into account when using the steel in the creep range.

In flue gases containing sulphur, the corrosion resistance is reduced. In such environments this steel can be used at temperatures up to 600-750°C (1110-1380°F) depending on service conditions. Factors to consider are whether the atmosphere is oxidizing or reducing, i.e. the oxygen content, and whether impurities such as sodium and vanadium are present.

Heat treatment

The tubes are delivered in heat treated condition. If another heat treatment is needed after further processing the following is recommended:

Stress relieving

850-950°C (1560-1740°F), 10- 15 minutes, cooling in air.

Solution annealing

1000-1100°C (1830-2010°F), 5-20 minutes, rapid cooling in air or water.

Welding

The weldability of Sandvik 8R40 is good. Welding must be carried out without preheating and subsequent heat treatment is normally not required. Suitable methods of fusion welding are manual metal-arc welding (MMA/SMAW) and gas-shielded arc welding, with the TIG/GTAW method as first choice.

For Sandvik 8R40, heat input of <1.5 kJ/mm and interpass temperature of <150°C (300°F) are recommended.

Bending

Annealing after cold bending is not normally necessary, but this point must be decided with regard to the degree of bending and the operating conditions. Heat treatment, if any, should take the form of stress-relieving or solution annealing, see under "Heat treatment".

Hot bending is carried out at 1100-850°C (2010-1560°F) and should be followed by solution annealing.

Applications

Sandvik 8R40 is used for super heater-tubes in steam power plants.

It is also frequently used for cooling tubes in ammonia converters, because of its good resistance to nitrogen absorption and good corrosion resistance.With its good hot-strength, and good resistance to hydrogen sulphide and intergranular corrosion, Sandvik 8R40 is a suitable material for furnace tubes in refineries. Furnace tubing used in vinyl chloride production is another example of applications in which this steel is often used.

Disclaimer: Recommendations are for guidance only, and the suitability of a material for a specific application can be confirmed only when we know the actual service conditions. Continuous development may necessitate changes in technical data without notice. This datasheet is only valid for Sandvik materials.